Images, for example, gradation images and monotone images such as characters and symbols, have hitherto been formed on a substrate by a thermal transfer method. A thermal dye transfer (thermal sublimation transfer) method and a heat-fusion (thermal ink fusion) transfer method have been extensively used as the thermal transfer method.
In the thermal dye transfer method among these methods, a thermal transfer film comprising a substrate and a dye layer, formed of a material prepared by melting or dispersing a sublimable dye as a coloring material in a binder resin, supported on the substrate is provided, this thermal transfer film is put on top of an image-receiving sheet, energy corresponding to image information is applied to a heating device such as a thermal head to transfer the sublimable dye contained in the dye layer in the thermal transfer film onto the image-receiving sheet and thus to form an image.
This thermal dye transfer method is advantageous in that the amount of dye transferred can be regulated on a dot basis by the quantity of energy applied to the thermal transfer film and, thus, excellent gradation images can be formed and characters, symbols and the like can be simply formed.
At the present time, various cards such as identification cards, driving licenses, membership cards, and ID cards have become widely used. Various types of information about identification of the holder and the like are recorded in these cards. In particular, in ID cards and the like, in addition to textual information such as address and name, a photograph image of the face is important, and the image should remain unchanged or undeteriorated for a long period of time, that is, should have good fastness properties (durability).
At the present time, the above thermal dye transfer method is adopted in information recording in such cards. In the gradation image and monotone image formed by the above thermal dye transfer method, however, since the transferred dye is present on the surface of the object, the image is poor in fastness properties such as fastness to solvents and plasticizers. For this reason, in cards required to have good fastness properties, such as ID cards on which a photograph image of the face has been recorded, an attempt to improve fastness properties of the image has been made (for example, Japanese Patent Laid-Open Nos. 156567/1995 and 240404/2002).
Japanese Patent Laid-Open No. 156567/1995 discloses a protective layer transfer film comprising a thermally transferable resin layer provided on a substrate film, characterized in that the thermally transferable resin layer comprises a transparent resin layer, a plasticizer-resistant resin layer, and a heat-sensitive adhesive resin layer stacked in that order from the substrate film side. This publication describes that an acrylic copolymer resin is used in the plasticizer-resistant resin layer. Japanese Patent Laid-Open No. 240404/2002 discloses a protective layer transfer sheet comprising a thermally transferable protective layer provided on at least a part of one side of a substrate sheet. This protective layer is a laminate having a multilayer structure of at least two layers, that is, comprises at least a layer composed mainly of an acrylic resin and a layer composed mainly of a polyester resin provided in that order on the substrate sheet. The claimed advantage of this construction is to improve fastness to plasticizer, water, fading and the like.
Further, it should be noted that, when a printed matter (for example, ID card) is passed through a detecting machine or the like, the protective layer undergoes physical friction. In this case, from the viewpoint of preventing the protective layer from being easily damaged or separated, it is desired that the protective layer have good fastness to abrasion and good adhesion to an object.
The fastness properties, particularly fastness to plasticizers, abrasion and the like, of the image formed on the object, however, are not yet satisfactory, and a further improvement in these properties is desired.
On the other hand, in addition to a conventional direct printing method in which thermal transfer is carried out onto a thermal transfer image-receiving sheet, a method using an intermediate transfer recording medium is known as the thermal transfer recording method.
The thermal transfer recording method of an intermediate transfer recording medium system is known also as a sublimation retransfer method. As shown in FIG. 3, in this method, a thermal transfer film 12 and an intermediate transfer recording medium 13 are put on top of each other. Upon heating using a thermal head 14, a dye is transferred from the thermal transfer film 12 onto a receptive layer in the intermediate transfer recording medium to once form a printed image 16 on the intermediate transfer recording medium 13. The intermediate transfer recording medium with the image 16 printed thereon is put on top of an object 17. The assembly is heated by a heat roller 18 from the substrate side of the intermediate transfer recording medium to transfer the printed image 16 formed on the intermediate transfer recording medium onto the object 17, for example, a card.
As shown in FIG. 4, the intermediate transfer recording medium basically comprises a transfer part on a substrate film 121, the transfer part having a three layer structure comprising a peel layer 122, a durable layer 123, and a receptive layer 124 provided in that order on the substrate film 121. Upon the transfer of the printed image 16 onto an object 17, the peel layer and the layers overlying the peel layer are stacked onto the object.
At the present time, various cards such as identification cards, driving licenses, membership cards, and ID cards have become widely used. Various types of information about identification of the holder and the like are recorded in these cards. In particular, in ID cards and the like, in addition to textual information such as address and name, a photograph image of the face is important, and the image should remain unchanged or undeteriorated for a long period of time, that is, should have good fastness properties. To meet this demand, a durable layer is formed in the intermediate transfer recording medium (for example, Japanese Patent Laid-Open No. 254840/2002). The fastness properties, particularly fastness to plasticizers, abrasion and the like, of the image formed on the object, however, are not yet satisfactory, and a further improvement in these properties is desired.